my vtx and vrx are 2.4 with11 dbi omni antennas,so i dont want to fly on the same frequency.i hve seen some posts mentioning that FLYSKY 35 mhz would be the best option for turnigy 9x to convert it into 72 mhz. but i dont see any online store selling it.kindly suggest if i have other options or a store online...!!

This is possible. I've done it myself. The only problem is the Turnigy 9x does not have an antenna mount soldered to the board. You can make one yourself with a piece of aluminum and a bolt, soldered or otherwise firmly attached to the pads on the board. Once you have the 72 MHz antenna mounted, you can then buy a JR 72 MHz module and stick it right in. That's all there is to it.

I've seen it for as low as $60 before. Despite what has been said by some folks on RCgroups, the synthesized module is compatible with the 9x. I believe the non-synthesized module is not, however. Will probably fry.